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            <div><h3 class="title">
                <a name="asio.reference.asynchronous_socket_operations"></a><a class="link"
                                                                               href="asynchronous_socket_operations.html"
                                                                               title="Requirements on asynchronous socket operations">Requirements
                on asynchronous socket operations</a>
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    <p>
        In this library, <span class="emphasis"><em>asynchronous socket operations</em></span> are
        those member functions having prefix <code class="computeroutput"><span class="identifier">async_</span></code>.
    </p>
    <p>
        For an object <code class="computeroutput"><span class="identifier">s</span></code>, a program
        may initiate asynchronous socket operations such that there are multiple
        simultaneously outstanding asynchronous operations.
    </p>
    <p>
        When there are multiple outstanding asynchronous <a class="link" href="read_write_operations.html"
                                                            title="Requirements on read and write operations">read
        operations</a> on <code class="computeroutput"><span class="identifier">s</span></code>:
    </p>
    <p>
        — having no argument <code class="computeroutput"><span class="identifier">flags</span></code>
        of type <code class="computeroutput"><span class="identifier">socket_base</span><span
            class="special">::</span><span class="identifier">message_flags</span></code>, or
    </p>
    <p>
        — having an argument <code class="computeroutput"><span class="identifier">flags</span></code>
        of type <code class="computeroutput"><span class="identifier">socket_base</span><span
            class="special">::</span><span class="identifier">message_flags</span></code> but where <code
            class="computeroutput"><span class="special">(</span><span class="identifier">flags</span> <span
            class="special">&amp;</span> <span class="identifier">socket_base</span><span class="special">::</span><span
            class="identifier">message_out_of_band</span><span class="special">)</span>
        <span class="special">==</span> <span class="number">0</span></code>
    </p>
    <p>
        then the <code class="computeroutput"><span class="identifier">buffers</span></code> are filled
        in the order in which these operations were issued. The order of invocation
        of the completion handlers for these operations is unspecified.
    </p>
    <p>
        When there are multiple outstanding asynchronous <a class="link" href="read_write_operations.html"
                                                            title="Requirements on read and write operations">read
        operations</a> on <code class="computeroutput"><span class="identifier">s</span></code> having
        an argument <code class="computeroutput"><span class="identifier">flags</span></code> of type
        <code class="computeroutput"><span class="identifier">socket_base</span><span class="special">::</span><span
                class="identifier">message_flags</span></code> where <code class="computeroutput"><span class="special">(</span><span
            class="identifier">flags</span> <span class="special">&amp;</span> <span
            class="identifier">socket_base</span><span class="special">::</span><span class="identifier">message_out_of_band</span><span
            class="special">)</span>
        <span class="special">!=</span> <span class="number">0</span></code>
        then the <code class="computeroutput"><span class="identifier">buffers</span></code> are filled
        in the order in which these operations were issued.
    </p>
    <p>
        When there are multiple outstanding asynchronous <a class="link" href="read_write_operations.html"
                                                            title="Requirements on read and write operations">write
        operations</a> on <code class="computeroutput"><span class="identifier">s</span></code>, the
        <code class="computeroutput"><span class="identifier">buffers</span></code> are transmitted in
        the order in which these operations were issued. The order of invocation
        of the completion handlers for these operations is unspecified.
    </p>
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